1. Field of the Invention
The present invention generally relates to a process of cleaning a semiconductor manufacturing system such as a plasma-enhanced chemical vapor deposition (or plasma CVD) system. More specifically, the present invention relates to a process of cleaning a manufacturing system adapted to form a fluorine-containing silicon oxide film (referred to as “FSG film”) such as an interlayer dielectric film of a semiconductor device. The present invention also relates to a method of manufacturing a semiconductor device. FSG stands for Fluorinated Silicate Glass.
2. Description of the Related Art
In general, a method of manufacturing a semiconductor device includes a plasma CVD process to form a semiconductor film on a substrate. Such film-formation process includes the steps of: placing a substrate on an electrostatic chuck provided in a reaction chamber; supplying a reactive gas into the reaction chamber; and applying high-frequency electric power between a pair of electrodes to generate a plasma and decompose the reactive gas molecules with the plasma, so that a semiconductor film is formed on the top surface of the substrate.
The film-formation process (deposition process) is repeated to manufacture a number of semiconductor devices. As the film-formation process is repeated, semiconductor films also accumulate on an inner wall of the reaction chamber and surfaces of the electrodes in the plasma enhanced CVD system. The semiconductor films deposited on the reaction chamber wall and electrodes may exfoliate and adhere to the substrate during the film-formation process. These semiconductor films contaminate the substrate.
Recently, therefore, a cleaning process is carried out to clean the inside of the reaction chamber of a plasma enhanced CVD system. The cleaning process uses a fluoride-based cleaning gas. In the cleaning process, a plasma is applied to the cleaning gas to generate fluorine atoms so as to clean (remove) films deposited on the inner wall of the reaction chamber and the surfaces of the electrodes. This cleaning process entails a problem that the fluorine atoms generated in the cleaning process are adsorbed on the inner wall of the reaction chamber and the surfaces of the electrodes, and remain there. Therefore, a fluorine-reducing gas is supplied into the reaction chamber to reduce and remove the residual fluorine atoms in the reaction chamber.
A specific example of a cleaning process is disclosed in Japanese Patent Kokai (Laid-Open Publication) No. 7-201738. In this cleaning process, active species (e.g., radicals or ions of nitride compounds) and a fluorine-reducing gas are supplied into the reaction chamber to cause the active species to act on the residual fluorine components, thereby reducing and removing the residual fluorine components.
Another cleaning process is disclosed in Japanese Patent Kokai No. 9-249976. This cleaning process uses NF3, CF4, C3F8, C2F6, or ClF3 as a fluoride-based cleaning gas, and uses at least one kind of gas selected from the group consisting of O2, H2 and an inert gas as a fluorine-reducing cleaning gas.
Japanese Patent Kokai No. 10-147877 discloses another cleaning process in which an inert gas (or a mixture of the inert gas and nitrogen gas) is supplied into the reaction chamber as a fluorine-reducing gas to reduce and remove residual fluorine components after or during the cleaning by use of a fluorine-based cleaning gas.
In the cleaning processes disclosed above, a ceramic cover having the same shape as that of a substrate or wafer is usually positioned on an electrostatic chuck provided inside the reaction chamber of a plasma enhanced CVD system in order to protect the surface of the electrostatic chuck. Silicon oxide films inside the reaction chamber are removed by supplying a fluoride-based cleaning gas into the reaction chamber and generating a plasma. After the cleaning, a fluorine-reducing gas is supplied into the reaction chamber to generate the plasma, with the ceramic cover being left on the electrostatic chuck, thereby reducing and removing residual fluorine atoms in the reaction chamber.
During the cleaning of the plasma enhanced CVD system, the ceramic cover is placed on the electrostatic chuck to protect the surface of the electrostatic chuck.
However, there is a problem in the conventional cleaning process. Warp of the ceramic cover, etc. produce a clearance between the ceramic cover and the electrostatic chuck and thus a fluoride-based cleaning gas enters the clearance to cause fluorine components to be adsorbed on the surface of the electrostatic chuck. The residual fluorine components, which have been adsorbed on the surface of the electrostatic chuck, cannot be sufficiently reduced and removed even when the radial components are subjected to the treatment using a fluorine-reducing gas. As a result, when forming a semiconductor film after the cleaning process, the residual fluorine components may separate from the surface of the electrostatic chuck (the phenomenon is referred to as “F degasification”) and decrease the film-forming (deposition) temperature in the vicinity of the substrate or wafer. This leads to problems including irregular film thickness, defective etching, and film flaking. These drawbacks are serious when forming an FSG film because significant F degasification occurs during the FSG film formation.